The present invention relates to multi-stage charge pumps suitable for use with integrated circuit applications.
Charge pumps and DC-to-DC converters have been used in the past in integrated circuit applications. See, for example, U.S. Pat. Nos. 5,781,473, 5,801,987, 5,553,030 and 5,216,588.
The charge pump described in U.S. Pat. No. 5,781,473 is a multi-stage charge pump, and the output of each of the stages is connected directly to the high voltage output of the charge pump. The charge pump stages can be configured to operate in parallel or in series, depending upon the state of various switches in the system.
The charge pump described in U.S. Pat. No. 5,801,987 is also a multiple stage charge pump in which one, two, three or four of the stages can be enabled. In the illustrated system, the outputs of all of the charge pump stages are connected to the output of the charge pump via respective diodes. These diodes bring with them the disadvantage of a voltage drop across the diode even when the diode is conductive.
By way of general introduction, the charge pumps described below are multiple stage charge pumps that are connected in series, with stage one directly connected to the high voltage output of the charge pump and stages two and three and progressively farther from the high voltage output of the charge pump. The charge pump stages are selectively enabled such that if charge pump stage m is enabled, then all charge pumps stages mxe2x88x921, . . . 1 are enabled. Depending upon the required output voltage, more or fewer of the charge pumps stages are enabled. This can be accomplished with a preprogrammed control circuit, or alternatively with an adaptive control circuit that responds to the output voltage of the charge pump. The embodiments described below are relatively easy to implement, and they avoid diode drops in the chain of series-connected charge pump stages.
This section has been provided by way of general introduction, and it should not be used to narrow the scope of the following claims.